The present invention relates to apparatus for limiting the force transmitted by a force transmitting member, in general, and to such apparatus for both limiting such force and to allow for disabling the drive means producing said transmitted force so long as the force to be transmitted exceeds a predetermined magnitude, in particular.
In many applications where force from a drive system is employed to, for example, drive a tool that performs a particular operation on a workpiece or to position a workpiece at an assembly machine workstation, it is desirable to provide means for limiting the force transmitted to the workpiece for such purposes in order to limit potential workpiece damage and/or to avoid the drive system damage that might result if the drive system is excessively overloaded. This is particularly true in an assembly machine having a multiplicity of workstations that derive all of their force requirements from a common force producing drive system. Failure to provide such force limiting means may result in damage to a plurality of successive workpieces and/or in drive system failure produced by, for example, the cumulative effects of several workstation overloads even though the load demands of a single workstation is well within the load handling capability of the drive system.
Numerous force limiting devices have been employed in the past for limiting the force provided by a drive source to less than some predetermined magnitude. One type of force limiting device employs a slip clutch for force limiting purposes while another type of device employs a force coupling spring that changes length to thereby limit transmitted force magnitude when the spring-coupled force exceeds some predetermined magnitude. While these devices served the purpose for which they were intended, they all are subject to certain undesirable limitations. One such limitation is that in these force limiting devices where the driven member is disconnected from the driving member, these members must be manually reconnected after the overload condition that caused these members to be disconnected from one another is removed. Another limitation with such prior art force limiting devices is that the disconnection of a driven member from a drive member occurs when there is an overload condition in one drive force direction only.
A primary object of the present invention is to provide a device for interrupting the drive force to a driven member for a driven member that can be driven in more than one drive force direction.
Another object of the present invention is to provide a device that will automatically restore the interrupted drive force to a driven member in more than one drive force direction once the overload causing said force interruption is removed.
A further object of the present invention is to provide overload sensing apparatus that includes a single overload signal generating electrical switch that will generate an overload signal for an overload occurring in more than one drive force direction.
Other objects, features and advantages of the present invention will be readily apparent from the following detailed description of the preferred embodiment thereof taken in conjunction with the accompanying drawings.